Markdown updates
This MR does the following:
- Uses the CI/CD Catalog for markdown linting, as opposed to a manual job
- Adds a linting exception file:
- Ignore line length limit (we already did this manually)
- Ignore requirment for first line to be H1
We find that the H1 heading is unnecessary in some templates, as the issue title itself meets this request. Also, using the CI/CD catalog is easy to maintain going forward and we should do that anywhere we are linting.